1. Field of the Invention
This invention relates to the treatment of materials that have been painted with lead-based paint to effect the removal of the paint in a safe and economical manner.
2. Description of the Prior Art
It has been established that paint containing lead compounds presents a health hazard, and its use in the United States has been banned since about 1978. Nevertheless much untreated lead paint is still in place; its removal is highly advisable and, in many installations, mandated by law. The reason for requiring removal of paint containing lead is that continued aging thereof causes it to flake and dust, increasing the potential for lead poisoning from inhalation.
There are presently available two methods for removing or stripping paint. One is physical and the other chemical. The physical method involves either sandblasting or destruction of the paint using heat from a blow-torch or hot air blower having an output temperature up to 1200.degree. F. This method is expected to be banned by the EPA shortly.
The chemical method involves two distinct classes of products and procedures. The most common products are those that contain an assortment of organic solvents, such as methylene chloride, toluene, acetone and various alcohols, that soften and/or dissolve whatever paint vehicle is encountered. Such products have been marketed for years. A number of these solvents are believed to be hazardous, having exhibited toxic and carcinogenic effects. Many of them have technical and economical disadvantages. The high volatility of these solvents severely restricts the time period allotted for removal of softened or dissolved paint, which rehardens shortly after application of the remover. Costs involved in removal and disposal of the tacky material produced by the solvents is relatively high. Solvent-type removers are restricted by seasonal and geographical conditions. Application of such removers outdoors in hot weather (above about 85.degree. F.), or in direct sunlight has been unsuccessful. Even though these products are said to include a film-former, the temperature of the painted substrate cannot exceed 100.degree. F. Above that temperature, the majority of solvent volatilizes prior to film formation, rendering the product ineffective.
A recently introduced line of products for chemically removing paint contain no organic solvents. These products are comprised principally of a combination of caustic compounds, such as calcium hydroxide, magnesium hydroxide, and sodium hydroxide. Such compounds are in a water base and generally form a paste. These products are applied to the painted material, and then allowed to dry for time periods as high as 48 hours. It is recommended by products of this type that the applied coating be covered with a polyethylene sheeting to retard drying and increase activity time. After drying is completed, a crusty residue, formed during drying, is scraped off laboriously. Thereafter, the substrate must be neutralized with an acid using precautionary procedures to prevent run-off from entering ground waters.
Problems attending the use of chemical or physical methods for removing oil-based, lead containing paints have led to use of modern paints and coatings which cover the oil-based, lead containing paints, thereby delaying the costly, removal thereof. Oil-based paints containing polyurethane, epoxy or alkyd resins, as well as latex paint, have been used for this purpose. The result of this approach is a composite paint system which must ultimately be removed to satisfy enviromental safety standards.
There remains a need in the art for a method wherein composite paint systems can be readily removed in a safe, economical manner using a single, low-cost formulation.